The present disclosure relates to an image pickup apparatus and a camera module in which a solid-state image pickup element (optical sensor) such as a CCD (charge coupled device) and a CMOS (complementary metal oxide semiconductor) image sensor (CIS) is configured as a chip scale package.
As a simple package method for an optical sensor, a chip scale package (CSP) structure has been proposed, and the optical sensor having the CSP structure is produced in volume.
Unlike a cavity package which is formed of ceramics or mold resin in related art, in the CSP structure, as a cavity structure having a partition wall between adjacent chips in unit of wafer, a Si wafer of a sensor unit and glass are bonded with resin.
Further, the CSP structure has a thru silicon via (hereinafter, referred to as TSV) formed therein, re-wiring is performed on a surface opposite to a sensor surface, a solder ball is attached, and the matter thus obtained is divided into pieces by dicing ultimately.
FIG. 1 is a diagram showing a basic structure of the cavity CSP structure.
In a CSP structure 1, as a sealing material for protecting an upper portion of a light receiving unit 21 on the front surface of an optical sensor (sensor chip) 2, a sealing glass (cover glass) 3 is disposed.
In the CSP structure 1, the sealing glass 3 is disposed on a peripheral portion excluding the light receiving unit 21 of the optical sensor 2 with a resin 4 intervened therebetween. Therefore, in the CSP structure 1, a cavity 5 is formed between the light receiving unit 21 of the optical sensor 2 and an opposed surface 31 of sealing glass 3 with respect to the light receiving unit 21.
In the CSP structure, an electrode 6 is formed with a TSV that penetrates the sensor chip from the front surface to the back surface thereof, thereby eliminating wirings using wire bond, which makes it possible to bond the glass in a clean room in a wafer state.
As a result, it is possible to attain a size reduction, a cost reduction, and a dustless condition as compared to a COB (Chip On Board) type package in related art.
However, in the CSP structure, in forming the TSV, if the cavity 5 is formed between the cover glass and the chip (optical sensor) as described above to reduce the thickness of the chip, when a thermal process such as reflow is carried out, a warp of the chip may undesirably occur due to an influence of a thermal stress.
This point will be described in more detail.
In the CSP structure shown in FIG. 1, to satisfy a condition of a via process of a deep-reactive ion etching (Deep-RIE) in forming the TSV on Si or an insulation film formation condition of CVD, an aspect ratio of a via diameter to an Si thickness has to be reduced for high productivity.
To attain this, the Si thickness is often reduced to approximately 50 to 100 μm in performing back grind (BG).
In the case where the optical sensor is small, a large warp is unlikely to occur in Si with a mechanical strength of Si. If the size of the optical sensor is increased, the warp WP is generated due to deflection in the back grind process in which a force is applied in a direction indicated by the arrow A of FIG. 2 or a stress with a substrate on which the CSP is mounted.
If the warp is generated, a position where a lens is focused is displaced optically in the center of the sensor and in the vicinity thereof. Therefore, in the case where the focus is positioned at the center, such a disadvantage that the vicinity blurs is caused.
As a method for overcoming this, as shown in FIG. 3, a CSP structure 1A with no cavity which is obtained by filling the cavity 5 with the resin 4 has been proposed. Hereinafter, the CSP structure with no cavity is referred to as a cavityless CSP structure in some cases.
By using the cavityless CSP structure with no cavity, it is possible to suppress the occurrence of the warp because the thermal stress generated in the cavity in the CSP structure having the cavity is significantly reduced.
That is, in the cavityless CSP structure, the warp due to the weakness in mechanical rigidity of Si of the cavity structure is not caused because the rigidity of glass is added to increase the mechanical rigidity by bonding Si with the glass having the thickness of 300 to 800 μm.
Further, in the cavity CSP structure, light is collected with a lens function using a difference between a refractive index of approximately 1.6 of an on-chip lens (OCL) formed of a resin material in the past and a refractive index of 1 of air.
In contrast, in the cavityless CSP structure, light collecting power is small in the refractive index of approximately 1.5 of the resin that fills between the glass and the sensor surface, and the sensitivity of the optical sensor is reduced. In view of this, in the cavityless CSP structure, a high refractive index of 1.7 to 2.1 is obtained by forming the OCL by using a material such as SiN, thereby achieving a structure which maintains the light collecting power.